KEY STEPS

Compendium on methods and tools to evaluate impacts of, and vulnerability and adaptation to, climate
change

LymSiM

Description

LymSiM simulates the population dynamics of the blacklegged tick, Ixodes scapularis, and
the dynamics of transmission of the Lyme disease agent, Borrelia burgdorferi, among ticks
and vertebrate hosts. LymSiM models the effects of ambient temperature, saturation deficit,
precipitation, habitat type, and host type and density on tick populations.

The model accounts for epidemiological parameters, including host and tick infectivity,
transovarial and transstadial transmission, such that the model realistically simulates the
transmission of the Lyme disease spirochete between vector ticks and vertebrate hosts. The software
features a dynamic life table model of Ixodes scapularis with a weekly time step; rates of
development, survival, fecundity, and host finding are based on weather or other environmental
variables and vary with time. The relationships used were based on the literature and unpublished
field studies.

Appropriate Use

Optimize control of Lyme disease and its vectors; and climate change impact studies.

Scope

The models are site-specific and require local surveys and weather data to parameterize them.

Key Output

Seasonal and geographical distributions of the Lyme disease agent and its vectors as a function of
climate.

A principal use of LymSiM has been to simulate and optimize the effects of management technologies
on populations of tick vector, Ixodes scapularis, and Borrelia burgdorferi in
eastern North America. The model was used to evaluate area-wide acaricide treatments, acaricide
self-treatment of white-footed mice and white-tailed deer, vegetation reduction, and white-tailed
deer density reduction. Simulations demonstrated that area-wide acaricide, vegetation reduction, or
a combination of these technologies would be useful for short-term seasonal management of ticks and
disease in small recreational or residential sites.

Moreover, acaricide self-treatment of deer appears to be the most cost-effective technology for use
in long-term management programs in large areas. Simulation results also suggested that deer
density reduction should be considered as a management strategy component. Finally, the model was
used to develop integrated management strategies for operational tick and tick-borne disease
control programs.

Based on the previous studies, the U.S. Centers for Disease Control and Prevention used LymSiM to
evaluate various Lyme disease control techniques as a function of various degrees of compliance by
the public involved in anti-tick measures. This assessment comparing the effectiveness of
alternative community-based prevention strategies illuminates the limitations and distributive
effects of interventions and helped clarify the actual available prevention options for community
residents.